Sound recording system



R. R. SCOVILLE SOUND RECORD ING SYSTEM Filed March 29, 1935 AMP AMP INVENTOR By R. R. SCOV/LLE ArrbRm-r f PatentedFeb. 12, 1935 l t r I i f -"vNI E TAT Y SOUND: RECORDING SYSTEM. Ray, R; scoville, Los, Angeles, Calif., assignorto Electrical Research Products, Inc., New York, N.Y., a corporation of Delaware l I o Applicationlylarch 29,1933, SierjialNo 663,274 v t t v j 9 Claims, 1 (Cl.1 '79 -100.3) t v This invention relates to recording systems and of=thetransmission of the positive print, that is." particularly to systemsin which the mean recordto the mean value of the scanningflux impressed. ingpositionof the recording device may "beat onxthe photocell or other reproducing device. some point other than the center of the available .An analogous relation has been foundin many; 5 range of the characteristic of the'medium'.v othenforms of recording. In'the present inven-, An objecttof the invention is-ito displace the tion, the-mean value of the-transmission of the mean recording position oi the recording. device positive print is small for smallamplitudes of the from the centerof the characteristic of the me record, and is increased to a normal value for dium when recording signals of smallamplitude, largerfamplitudes of the record; If the photo.- thus reducing the carrying capacity of the system.- graphicprocesses donot create any distortion, the.

Another object of the invention is to restore light flux trans 'tted through the positive print. the mean recording position of the recording dewill be proportional to the light flux originallyim-,; vice to the center of thecharacteristic of'the mepressed on the photographio record,- or, inother dium when the amplitude of. the signals exceeds words, thegexposure of thenegative record is pro-.- a predetermined value thus increasingthe carryportionalto the transmission of the positive print. 15 ing apacity of the system to normal. 1 :IIL accordance withthev present invention, the A feature ofithe invention resides ina control recording'deviceis mechanicallyadjusted so that circuitvcontaining an element which is substantheimean v'alueor position iofthe recording flux tially unaffected by signalsof a range of small: is inwthe centerofthe available rangeof the amplitudes,'but is materially'alteredin'its action selectedxpcharacteristic ofthe: negative film. A1 by signals :hav'ing anam'plitude exceeding aprecontrollable biasv is then*applied to the recording, determined value. H u device todisplace themean v lue or position of Forconvenience, the invention has'been disthe recording flux iromthe center of the available closed embodied in a system for recording r'riodurangeto the lower end of the range of the charlated'ccurrents on a photographic medium. It acteristicp. Theexposureof the negative is thus will be apparent to those skilled in the art that reduced to some small value; Modulated cur,-

the invention is applicable to the recording of the rents havinga maximum amplitude less than the variations. in. any type of current, and is also valuedetermined by this adjustment maythen be applicable to recording systems using recording recorded but due tothe small exposure, avery 30. mediums other than a photographic film, such as light: negative will be produced andthe positive a magnetized tape or engraved wax. 1 print will be correspondingly dark. a 1' In known recording systems, the recording de A control circuit energized by the modulated vice operates over a suitable range of someselecte'd currents, oontrols the magnitude of the biasing characteristic of therecording medium. The currentappliedto the recording device; Aknown selected characteristic may be, for example, a type of thermionic amplifier, filled with one of the lateral movement .in a waxysubstanceavertical rare gases; is connected in thecontrol circuit: movement in awaxysubstance,a variation" of When the "amplitude ofthe modulated currents the magnetic effect produced in a magnetic maexceedsa certain value determined by the char terial, a variation in thea'rea of a photographic acteristics of this gas-filled amplifier, the ampli- 40 medium exposed to a recording light, or a variafier breaksfdown, a large current flows and retion in the degree of exposure of a photographic dtices the effect of thebiasing current to zero, medium. In known systems, the recording" de- 1 thus restoring the recording device to the condivice is so adjusted that, in the absence of current tion determined by its mechanical adjustment to be recorded, the mean recording position is" in and increasing the exposure of thenegative to the the center of the selected characteristic; andvis value at thefcenterof the characteristic. When 14 varied above and below this center position bythe the amplitude of the modulated currents again variations in thecurrent to be recorded. t falls to a small value, a second gas filled amplifier As the known types of recording .mediums are is actuated and'restores the ampifier first actunot perfectly homogeneous, a certainamount of ated. The effect of the biasing current is thus noise is produced duringthe reproduction of the restored to its ihitialvalue, and the: exposure ,0

record; due to the irregularitiesin the original thenegative record again reduced to asmall record and in the copy reproduced. Experiments value. have shown that the noise currents produced dur- The drawingshows in diagrammatic form a" ing the reproductionof a positive print of a photofilm sound recordingsystem including a preferred v graphic record are proportional to the mean value] form 0f the invention. i

' T. E. Shea,

For convenience of description, a film sound recording system using a ribbon light valve has been disclosed. The invention is not thereby to be limited to the specific type of recorder disclosed, but is obviously applicable to anyother suitable recorder operating on any suitable medium, such as a magnetized tape or wax record, and may be utilized to record the variations in any type of signal currents. The specific type of light valve disclosed is described in detail in an article The principles of the light valve by W. Herriott and W. R. Goehner, published in the Journal of the Society of Motion Picture Engineers vol. XVIII, pages 697-730, June, 1932. H

Light from a suitable source 1 is focussed by a lens system 2 through aligned apertures 3 pierced in the pole faces of a permanent magnet 4. The light emerging from the aperture 3 is focussed by a lens system represented by the lens 5on a film 6 moved at constant speed in a known manner by the sprocketst7, 8 or other suitable means; An opaque plate 9 pierced by a'small aperture 10 limits the exposed area of the film 6. A pair of conductive ribbons 11, 12, which may be parts of a single ribbon, limit the height lengthwise of the film of theimageformedby the re-, cording beam. The ribbons 11, 12 are so mounted and supportedthat, in the absence of any current flowing in'the ribbons, the. image produced on the moving film will product an exposurein the center of the range of the characteristic to beusedinrecordihg. When an .electric current flows in the ribbons 11, 12, the reaction of the magnetic field produced by this current with the steadyfield produced by the magnet 4 will cause adisplacement of the ribbons 11, 12 proportional to the 'current, increasing or decreasing the height of the image formed on the film 6 and thusvarying the time of exposure of the film-6 to the recording beam.

Acoustic waves are detected by a suitable detector, such as the microphone 13, which thus becomes a source of signal currents. The signal currents may be amplified in suitable amplifiers 14 and 15. A portion of theamplified signal currents is applied through transformer 16 and car pacitor 17 to the ribbons 11', 12 of the'light valve,

, and causes the ribbons 11, 12 of the light valve to oscillate in accordance with the variations in thesignal currents.

A portion of the amplified signal currents is applied through transformer 18 to a rectifier 19. The rectifier 19 has, for convenience, been disclosed as a three-element vacuum tube or thermionic triode,but it will be obvious that-many other rectifiers, such. as a copper-oxide-copper couplamay be used. A battery 20 impresses a instantaneous suitable negative potential on the control elec trode of the triode 19. The'cathode of the triode 19 maybe heated by a battery 21, or other suitable source of current. The triode 19. may be adjusted to produce rectification in .the control electrode-cathode. circuit, with subsequent amplification in the anodeecathode circuit or to produce partial or complete rectification by the conjoint action of the control electrode-cathode circuit'and the anode-cathode circuit.

Current from a suitable source, such as battery 22, fiows through wire 23, resistor 24, resistor 25, inductor 26,-anode-cathode circuit of'triode 19 back to battery 22. This current will cause the upper end of resistor 24 to become more positive than the lower end, and the upper end of resistor 25 to become more negative than the lower .540, September, 1931.

inductor 26, form a low-pass filter and cause the a current flowing in resistors 24and 25 to vary only with the envelope of the variations in the signal currents. 1,- l

The control devices 29 and 30jare gas-filled three-element vacuum tubes, or trionodes, such as briefiy described in an article A method of obtaininga linear time axis for a chathode ray oscillograph by A. L. Samuel, published in The Review of Scientific Instruments, vol. 2, pages 532 The trionode may be of the same general dimensions and appearance as the triodes in general use in radio receiving sets, but is filled with some suitable gas, such as argon, at a low pressure. The characteristics of the trionode are such that, for any given anode potential, there is acritical control-electrode potential. .If the control-electrode potential with re-. spect to the cathode is more negative than the critical value, the anode-cathode current is small and is usually substantially zero. If the controlelectrode potential with respect to the cathodeis less negative than the critical value, the anodecathode current is no longer influenced by the control-electrode potential, a visible discharge occurs-between anode and cathode, and the anodecathode current is determined by the potential between anode and cathode andby the resistance in the anode-cathode circuit. While the visible discharge continues, the potential drop insidethe trionode between anode and cathode is of the order of the ionizing potential of the gas and will generally be some 15 to 25 volts.- 'The potentials required to produce the visible discharge are generally rather critical. To restore the trionode to the non-discharging condition, afterap.-.

plying a negative potential larger than the critical value to the control electrode,-the anodea cathode potential must be interrupted or annulled for a short time. The potentials required to restore in trionode to the non-dischargingv condition are, in general, less criticalthanithe potentials required to produce the discharge.

The battery 31 is of such potential that, inzthe.

the trionode 29, resistor .33, inductor 34', wire 35, ribbons l1 and 12 of the light va1ve,wire 36 to battery 32. The current flowing in the ribbons 11, 12 causes the ribbons 11, 12 to be drawn together, thus reducing the mean time of exposure of the film 6 and the load carrying capacity of thelight valve. By adjustingthe resistance 33, the current flowing in the ribbons 11, 12 and the reduction in the the light valve may load carrying capacity of bonsill, 12 is about one-third of the spacing determined by the mechanical adjustment;

The battery 37 is of suchpotential that," in the be adjusted. For general use,-the current is adjusted so that, in the ab'" sence of signal currents, the spacing of the rib-' applied to the sys tem, the rectified current flowing in the resistor 25 increases the negative potential applied to j the control electrode of the trionod'ef29 whi1e the current flowing inresistor 24 decreases the potential applied to thecontrol electrode of the trionode 30. So long as the signalcurrents have an amplitude less than a certain value, the steady current applied to the -ribbons ll, 12 will remain unchanged; The signal-currents applied by the transformer 16 will cause 'the rib-k bons 11, 12 to vibrate and vary the time of exposure of thefilm 6 thus-producing a record "of the signal currents. i.

Although the anode-cathode 'current 'of the trionode SOissubstantially zero, current from the battery 38 can'flow through =resistor39, and bat t'eries 41, 31, 37, 42 to battery 38, thus'charging.-

the capacitor 40. a When the signal currentsincrease toan -am-w plitude such that the potential developed acrossresistor 24 reduces the potential applied to theto less than the critical value, thel trionode 30 trionode 30 W111 break downand thecapacitor'40 and the} can then discharge throughresistor33 anode-cathode circuit of trionode 30. Current frornbattery 38 can 39 and 33 and the trionode 30.

anode-cathode I circuit of the resistor 33 which reduces the anode potential of the trionode 29 and stops the discharge through trionode 29. The steady current applied to the ribbons ll, 12 decreases to zero and the mean spacing of the ribbons increases to the value determined by the mechanical adjustment. The load carrying capacity of the valve thus increases to its maximum value.

So long as the potential applied by the battery 31 together with the potential difference due to the rectified signal currents flowing in the resistor 25 maintains the control-electrode of the trionode 29 more negative than the critical potential, the trionode 29 cannot discharge. When the signal currents again fall to a small value, the rectified current flowing in resistors 24 and 25 will decrease to a small value, and

the trionode 29 will break down and reestablish the steady current through the ribbons ll, 12, thus reducing, the load carrying capacity of the light valve to its former small value.

trionode 30, will become more negative than the critical value. As the discharge current of the trionode 30 must pass through the resistors 39 and 33, if the resistance of the resistor 39 is large,

the discharge current will be small and the large negative potential appliedto the control electrode will stop the discharge, restoring the whole control circuit to the initial conditions; i

What is claimed is: i

, 1. In a recording system, a source of signal currents, a recording medium, a recording de-- vice actuated by said signal currents and mechanically adjusted to normally produce a record about a desired point in the available characteristic of said medium, a control circuitcou pled to said device, means in said control circuit for electrically displacing said device from said normal point to produce a record about a second recording point throughout a predetermined range of small amplitudes of said signal currents,

and other means in said circuit actuated only by signal currents having amplitudes outside said range to neutralize the effect of said first means.

2. In a recording system, a source of signal currents, a recording medium, a recording device actuated by said signal currents and mechanicalforsupplying current "device for 1 displacing said device from said realso flow through. resistors This sudden spurt of current in resistor 33 produces a drop of potential across The po-: tential applied to the control electrode of the lyadjustechtofinorrnally produce arecord about apredetermined point in the characteristic *of i device, means in said control circuit forcelec trically' displacing said device from said normal point to produce a record about asecondfrecording point i throughout a predetermined range-of small amplitudes of said signal currents, means in *s'aidf'circuit actuated" only by signal currents; having" amplitudes outside said range to neutral-' saidcircuit' for rendering said neutralia'ationiim efiective when the amplitude of 'saidsignal currents is within 1 said predetermined range.

3. In a recording system, a source of signal cur-f said medium, a control circuit coupled to said 10. ize the effect "oi said first means and'means in rentsga grecording medimn,: 'a' recording device actuatedby' saidsignal currents andmechanically adjusted-to normally produce a record about a desired point in the available characteristic of said medium, a control circuit coupled to said device, a source or curr from said sourceto said cording point to produce a record about a second recording point; "m'eans responsiveto signal currents exceeding, a predetermined range of small amplitudesto reduce said current to a small value, and other means in said circuit responsive to signal currents within said ranjge of amplitudes for restoring said displacing current to its original value.

i 4. Inya. recording system, a source of signal currents, a recording medium, a recording device actuated by said signal currents and mechanically adjusted to produce a record about a desired point in the characteristic of said medium, a

ent in"csaid circuit, means control circuit coupled to said device, a source i of unidirectional current, means for supplying current from said source fordisplacing said device from said recording point, a gas-filled ionic device responsiveto signal currents exceeding a predetermined range of amplitudes toreduce' said unidirectional current to a small value, and a second gas-filled ionic device responsive-to sig nal currents within said range torestore said first ionic device to its originalfcondition.

, 5. In a recording system, a source of signal currents, a recording medium, a recording device actuated by signal currents, a gas-filled ionic device, a circuit for applying a potential of less than the critic al value to the control electrode of said ionic device, a source of current in serial relationwith said recording device and the anode-cathode circuit of said ionic device whereby the discharge through said ionic device reduces the load carrying capacity of said recording device, a second circuit for applying a potential derived from said signal currents to said control electrode, a second gas-filled ionic-device, a third circuit for applying a potential exceeding the critical value to the control electrode of said second ionic device, a fourth circuit for applying a potential derived from said signal currents to the control electrode of said second ionic device whereby when the amplitude of said signal cur rents exceeds a predetermined value said second ionic device will discharge and reduce-thedischarge through said first ionic device to a small value thus increasing the load carrying capacity of said recording device. I

6. In a recording system, a source of signal currents, a recording medium, a recording device I p actuated by signal currents to produce a record in said medium, a gas-filled ionic device, a circuit for applying a potential of less than the critical value 41 to. the. control electrode of" said .ionic device, a source of current in serial relation with said recording device, the anode-cathode circuit of said source of current in serial relation with the-anode-- cathode circuit of said second ionic device, said resistor and a second resistor, a capacitor in par-q allel relation with said second resistor, and a third circuit for applying potentials derived from the potentials apsaid signal currents to reduce plied to the control electrodesof both said ionic devices.

7, In a recordingsystem, a source of signal cur-; rents, a recording medium, a recording device ac-1 tuatedby'signal currents to produce a record in said medium, a gas-filled ionic device, a circuit for applying a potential of less thanthev criticalvalue to the control electrode of said ionicrdevice, a;

7 source of current in; serial relation with-said ree cording device, the anode-cathode circuit of said ionic device and a resistor, a second gas-filled ionic device, a second circuit for applying a poten-,- tial exceeding the criticalvalue to the controlelectrode, of said second ionic device, a second source of current in serial relation with theanodecathode circuit of said second ionic device, saidresistorlandfa second resistor, a capacitor in parallel relation uwith said second resistor, a third resistor in the j control electrode-cathode circuit of. said first ionic device, a fourth resistor in the control,electrode-cathodecircuit of said second ionic device,said third and fourth resistors being in. serial relation, and a a circuit for supplying rectified signalcurrents to said third and fourth resistors, a U

8. In a recording system, a recording medium, a

source of signal i currents, a recording device actuated vby signal: currents, a control circuit coupled to said. device and means in said control circuit including-a-plurality of ionic devices for displacing the recording point of said devicegin predetermined steps. r

, 9.,-In'a recording system, a recording medium, a. source. of signal currents, arecording device actuated by signalcurrents, a control circuit coupled to said device, means in said control [circuit including anionicdevice actuated by signal currents within-a, predetermined range of amplitudes for displacing the recording point of said,

device in steps, and other means including an ionicdevice .actuated bysignal currents having amplitudes outside said range to restore the recording point of said devic RAY R, SCOVILLE. 

